• NAME
  
  pthread_create - create a new thread
• SYNOPSIS
  

  
   #include <pthread.h>
  
   int pthread_create(pthread_t * thread , const pthread_attr_t * attr ,
                       void *(* start_routine ) (void *), void * arg ); 
  
    Compile and link with -pthread.
  
  
  

• DESCRIPTION
  
  The
  pthread_create ()
  function starts a new thread in the calling process.
  The new thread starts execution by invoking
  start_routine ();
  arg
  is passed as the sole argument of
  start_routine ().
  
  The new thread terminates in one of the following ways:
  

  *
  

  It calls
  pthread_exit(3) ,
  specifying an exit status value that is available to another thread
  in the same process that calls
  pthread_join(3) .
  

  *

  It returns from
  start_routine ().
  This is equivalent to calling
  pthread_exit(3)
  with the value supplied in the
  return
  statement.
  

  *

  It is canceled (see
  pthread_cancel(3) ).
  

  *

  Any of the threads in the process calls
  exit(3) ,
  or the main thread performs a return from
  main ().
  This causes the termination of all threads in the process.
  
  
  
  The
  attr
  argument points to a
  pthread_attr_t
  structure whose contents are used at thread creation time to
  determine attributes for the new thread;
  this structure is initialized using
  pthread_attr_init(3)
  and related functions.
  If
  attr
  is NULL,
  then the thread is created with default attributes.
  
  Before returning, a successful call to
  pthread_create ()
  stores the ID of the new thread in the buffer pointed to by
  thread ;
  this identifier is used to refer to the thread
  in subsequent calls to other pthreads functions.
  
  The new thread inherits a copy of the creating thread's signal mask
  The set of pending signals for the new thread is empty
  The new thread does not inherit the creating thread's
  alternate signal stack
  
  The new thread inherits the calling thread's floating-point environment
  
  The initial value of the new thread's CPU-time clock is 0
  (see
  pthread_getcpuclockid(3) ).
  
  Linux-specific details
  The new thread inherits copies of the calling thread's capability sets
  (see
  capabilities(7) )
  and CPU affinity mask (see
  sched_setaffinity(2) ).
  

• RETURN VALUE
  
  On success,
  pthread_create ()
  returns 0;
  on error, it returns an error number, and the contents of
  *thread
  are undefined.
  
• ERRORS
  

  EAGAIN

  Insufficient resources to create another thread,
  or a system-imposed limit on the number of threads was encountered.
  The latter case may occur in two ways:
  the
  RLIMIT_NPROC
  soft resource limit (set via
  setrlimit(2) ),
  which limits the number of process for a real user ID,
  was reached;
  or the kernel's system-wide limit on the number of threads,
  /proc/sys/kernel/threads-max ,
  was reached.
  

  EINVAL

  Invalid settings in
  attr .
  

  
  

  EPERM No permission to set the scheduling policy and parameters specified in
  attr .
  

• CONFORMING TO
  
  POSIX.1-2001.
  
• NOTES
  
  See
  pthread_self(3)
  for further information on the thread ID returned in
  *thread
  by
  pthread_create ().
  Unless real-time scheduling policies are being employed,
  after a call to
  pthread_create (),
  it is indeterminate which thread--the caller or the new thread--will
  next execute.
  
  A thread may either be
  joinable
  or
  detached .
  If a thread is joinable, then another thread can call
  pthread_join(3)
  to wait for the thread to terminate and fetch its exit status.
  Only when a terminated joinable thread has been joined are
  the last of its resources released back to the system.
  When a detached thread terminates,
  its resources are automatically released back to the system:
  it is not possible to join with the thread in order to obtain
  its exit status.
  Making a thread detached is useful for some types of daemon threads
  whose exit status the application does not need to care about.
  By default, a new thread is created in a joinable state, unless
  attr
  was set to create the thread in a detached state (using
  pthread_attr_setdetachstate(3) ).
  
  
  
  On Linux/x86-32, the default stack size for a new thread is 2 megabytes.
  Under the NPTL threading implementation, if the
  RLIMIT_STACK
  soft resource limit
  "at the time the program started"
  has any value other than "unlimited",
  then it determines the default stack size of new threads.
  Using
  pthread_attr_setstacksize(3) ,
  the stack size attribute can be explicitly set in the
  attr
  argument used to create a thread,
  in order to obtain a stack size other than the default.
  
• EXAMPLE
  
  The program below demonstrates the use of
  pthread_create (),
  as well as a number of other functions in the pthreads API.
  
  In the following run,
  on a system providing the NPTL threading implementation,
  the stack size defaults to the value given by the
  "stack size" resource limit:
  
  

  
  8192            # The stack size limit is 8 MB (0x80000 bytes)
  
  
  Thread 1: top of stack near 0xb7dd03b8; argv_string=hola
  
  
  Thread 2: top of stack near 0xb75cf3b8; argv_string=salut
  
  
  Thread 3: top of stack near 0xb6dce3b8; argv_string=servus
  
  
  Joined with thread 1; returned value was HOLA
  
  
  Joined with thread 2; returned value was SALUT
  
  
  Joined with thread 3; returned value was SERVUS
  
  
  
  
  
  In the next run, the program explicitly sets a stack size of 1MB (using
  
  
    pthread_attr_setstacksize(3) )
  
   for the created threads:
  
  
  
  
  
  
  Thread 1: top of stack near 0xb7d723b8; argv_string=hola
  
  
  Thread 2: top of stack near 0xb7c713b8; argv_string=salut
  
  
  Thread 3: top of stack near 0xb7b703b8; argv_string=servus
  
  
  Joined with thread 1; returned value was HOLA
  
  
  Joined with thread 2; returned value was SALUT
  
  
  Joined with thread 3; returned value was SERVUS
  
  
    Program source
  
   
  
  
  
  #include <pthread.h>
  #include <string.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <errno.h>
  #include <ctype.h>
  
  #define handle_error_en(en, msg) \
          do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
  
  #define handle_error(msg) \
          do { perror(msg); exit(EXIT_FAILURE); } while (0)
  
  struct thread_info {    /* Used as argument to thread_start() */
      pthread_t thread_id;        /* ID returned by pthread_create() */
      int       thread_num;       /* Application-defined thread # */
      char     *argv_string;      /* From command-line argument */
  };
  
  /* Thread start function: display address near top of our stack,
     and return upper-cased copy of argv_string */
  
  static void *
  thread_start(void *arg)
  {
      struct thread_info *tinfo = (struct thread_info *) arg;
      char *uargv, *p;
  
      printf("Thread %d: top of stack near %p; argv_string=%s\n",
              tinfo->thread_num, &p, tinfo->argv_string);
  
      uargv = strdup(tinfo->argv_string);
      if (uargv == NULL)
          handle_error("strdup");
  
      for (p = uargv; *p != (aq\0(aq; p++)
          *p = toupper(*p);
  
      return uargv;
  }
  
  int
  main(int argc, char *argv[])
  {
      int s, tnum, opt, num_threads;
      struct thread_info *tinfo;
      pthread_attr_t attr;
      int stack_size;
      void *res;
  
      /* The "-s" option specifies a stack size for our threads */
  
      stack_size = -1;
      while ((opt = getopt(argc, argv, "s:")) != -1) {
          switch (opt) {
          case (aqs(aq:
              stack_size = strtoul(optarg, NULL, 0);
              break;
  
          default:
              fprintf(stderr, "Usage: %s [-s stack-size] arg...\n",
                      argv[0]);
              exit(EXIT_FAILURE);
          }
      }
  
      num_threads = argc - optind;
  
      /* Initialize thread creation attributes */
  
      s = pthread_attr_init(&attr);
      if (s != 0)
          handle_error_en(s, "pthread_attr_init");
  
      if (stack_size > 0) {
          s = pthread_attr_setstacksize(&attr, stack_size);
          if (s != 0)
              handle_error_en(s, "pthread_attr_setstacksize");
      }
  
      /* Allocate memory for pthread_create() arguments */
  
      tinfo = calloc(num_threads, sizeof(struct thread_info));
      if (tinfo == NULL)
          handle_error("calloc");
  
      /* Create one thread for each command-line argument */
  
      for (tnum = 0; tnum < num_threads; tnum++) {
          tinfo[tnum].thread_num = tnum + 1;
          tinfo[tnum].argv_string = argv[optind + tnum];
  
          /* The pthread_create() call stores the thread ID into
             corresponding element of tinfo[] */
  
          s = pthread_create(&tinfo[tnum].thread_id, &attr,
                             &thread_start, &tinfo[tnum]);
          if (s != 0)
              handle_error_en(s, "pthread_create");
      }
  
      /* Destroy the thread attributes object, since it is no
         longer needed */
  
      s = pthread_attr_destroy(&attr);
      if (s != 0)
          handle_error_en(s, "pthread_attr_destroy");
  
      /* Now join with each thread, and display its returned value */
  
      for (tnum = 0; tnum < num_threads; tnum++) {
          s = pthread_join(tinfo[tnum].thread_id, &res);
          if (s != 0)
              handle_error_en(s, "pthread_join");
  
          printf("Joined with thread %d; returned value was %s\n",
                  tinfo[tnum].thread_num, (char *) res);
          free(res);      /* Free memory allocated by thread */
      }
  
      free(tinfo);
      exit(EXIT_SUCCESS);
  }
  
  

• BUGS
  
  In the obsolete LinuxThreads implementation, each of the threads in a process has a different process ID. This is in violation of the POSIX threads specification, and is the source of many other non-conformances to the standard; see pthreads(7) .
• SEE ALSO
  
  getrlimit(2) , pthread_attr_init(3) , pthread_cancel(3) , pthread_detach(3) , pthread_equal(3) , pthread_exit(3) , pthread_getattr_np(3) , pthread_join(3) , pthread_self(3) , pthreads(7)
• COLOPHON
  
  This page is part of release 3.19 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

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